Sertoli cells are the epithelial "nurse" cells of the testis which along with the germ cells comprise the seminiferous tubules. The Sertoli cells clearly play important although incompletely defined roles in the process of spermatogenesis. The long term goals of this project are to understand the different roles of the Sertoli cells in spermatogenesis. These goals relate directly to human health problems dealing with reproductive infertility and may lead to new approaches to contraception. In the past grant periods this project has focused on the characterization of Sertoli cell secretion products and their specific roles in spermatogenesis. In the next grant period we propose logical and focused extensions of our previous studies, and, in addition, propose some new approaches to understanding how Sertoli cells products influence germ cells. The specific aims for the next grant period include: 1. The identification and characterization of regulatory elements on the FSH receptor (FSHR) gene promoter. 2. Identification of agents which regulate the expression of the FSH receptor in Sertoli cells in culture and in vivo. 3. Successful direction of transgenes into the Sertoli cells of transgenic mice. We hope that this last aim will lead to ways to specifically alter the expression of genes in Sertoli cells in vivo.